The Pont du Gard is one of the archeaological wonders of France, and it is a designated World Heritage site.
The three tiered aqueduct crosses the Gardon River, and at 169 feet high it is the tallest of all the Roman elevated aqueducts. It is worth paying the extra for a guided tour as that way you get to walk along the water channel at the very top of the aqueduct which is quite an eye opener. The sheer precision of the engineering is quite staggering. The bridge is part of an aqueduct that was originally 50Km in length, ending in Nimes. The drop over that 50Km was only 12 metres, an average gradient of only 24cms per kilometre or a quarter of a millimetre per metre - that's almost perfectly flat and yet it was enough for the water to flow to Nimes by gravity. Beyond the bridge, through the arches you may be able to make out the ominous build up of cloud that was to turn into a right old thunderstorm later in the evening.